Interpretive Summary: Fruit flies attack hundreds of fruits and vegetables and cause trade restrictions wherever they occur. The mass release of parasitoids, small wasps that develop in and ultimately kill immature flies, is an effective and environmentally-friendly means of controlling fly numbers, particularly in sensitive areas such as urban settings and parks. However, some species seem to require additional chemical cues from fruit in order to lay eggs in fly-hosts contained in artificial mass-rearing devices. This makes rearing difficult, laborious and expensive. Scientists at the USDA-ARS Center for Medical, Agricultural and Veterinary Entomology in cooperation with colleagues from EMBRAPA (Brazil) and the Instituto de Ecologia (Mexico) have identified a compound produced by the fly larvae themselves that acts as an egg-laying stimulant and is sensed in part through the parasitoids’ ovipositor. This chemical, in addition to other being investigated, may be part of a solution that could be cheaply applied to mass-rearing devices to improve parasitism rates and increase the numbers of parasitoid species that can be used for augmentative biological control.

Technical Abstract:
Tephritid fruit fly parasitoids use fruit-derived chemical cues and the vibrations that result from larval movements to locate hosts sequestered inside fruit. However, compounds produced by the larvae themselves have not been previously described nor their significance to parasitoid foraging determined. We collected the volatiles from four species of tropical/subtropical Tephritidae (Anasterpha suspensa (Loew), Bactrocera dorsalis (Hendel), Bactrocera cucurbitae (Coquillett) and Ceratitis capitata (Weidimann)), representing two subfamilies (Dacinae and Tryptinae). Para-ethylacetophenone was a major constituent of all four, and was not associated with larvae of another acalypterate fly, Drosophila melanogaster Meigen, or with the calypterate Musca domestica L.. It was also present in volatiles from whole, A. suspensa infested fruits of Eugenia uniflora (L.). While collected in this study as a volatile, it was presumably also present in the fluid surrounding larvae inside fruit. Para-ethylacetophenone was not necessarily produced as a direct consequence of fruit consumption since it was also detected from larvae that developed in two artificial diets and in “spent” diets subsequent to larval development. Sensillae on both the antennae and ovipositor of the opiine braconid fruit fly parasitoid, Diachasmimorpha longicaudata (Ashmead) responded to para-ethlacetophenone in larval volatiles and as a synthetic. While a potential cue to foraging parasitoids, para-ethylacetophenone showed no long range (>1m) attractiveness to the parasitoid, but did stimulate ovipositor-insertion and oviposition into both a natural (fruit) and an artificial (parafilm) substrate. Thus it may prove useful in colonizing and mass-rearing opine fruit fly parasitoids.